1. Field of the Invention
The invention concerns cosmetic emulsion compositions formulated with inorganic sunscreens stabilized against color and viscosity degradation.
2. The Related Art
Sunscreen compositions are commonly used during outdoor work or leisure. They protect exposed skin against sunburn, cancer and even photoaging. In general, sunscreen preparations are formulated as creams, lotions or oils containing as active agent an ultraviolet radiation absorbing or at least reflecting chemical compound.
The ideal sunscreen formulation should be non-toxic, non-irritating to skin tissue and capable of convenient application in a uniform continuous film. The sunscreen active agent as well as the composition into which it is formulated should be sufficiently chemically and physically stable. An acceptable shelf life is required for extended storage.
Chromophoric organic sunscreen agents are generally the most effective. Unfortunately many of these organic actives cause adverse allergic reactions. It is therefore desirable to minimize the level of such materials.
Inorganic ultrafine particulate compounds such as zinc oxide and titanium dioxide have been employed as sunscreen agents. Illustrations of this technology are found in U.S. Pat. No. 5,215,749 and U.S. Pat. No. 5,188,831, both to Nicoll et al. Inorganics are not known as sensitizers generating allergic reactions. However, stability of such formulations is a noticeable problem. Adverse effects include viscosity buildup and discoloration under extended storage conditions. These adverse consequences can be particularly pronounced in emulsions which are of the oil continuous variety.
Accordingly, there remains a need to uncover inorganic sunscreen particulate containing formulations of increased storage stability, particularly compositions resistant to significant changes in viscosity and color.